fix v2 conversion to ensure we provide blocks in correct format

[antiochp]

Testing on testnet (was floonet) uncovered an issue in our protocol version handling when providing blocks to v2 peers.

I think we see this on testnet because there are relatively few nodes in sync.
This does not appear to be happening on mainnet but I suspect this is simply masked by the fact we have better connectivity and more peers available.

The following error occurs when attempting to provide a full block to a v2 peer -

20201007 14:54:15.459 DEBUG grin_p2p::conn - try_break: exit the loop: Serialization(UnsupportedProtocolVersion)

This is because we store v3 CommitOnly blocks in the local db and the bug resulted in us not converting the block into v2 compatible format prior to the serialization attempt. We do not have "input features" and cannot serialize successfully.

• We need to do the conversion if the peer is v2.
• For v3 peers and above we do not need to convert.

The bug had this logic flipped.

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This would most obviously manifest itself if a 4.0.0 node attempted to sync against a number of 4.1.0 nodes.
Given 4.1.0 is the latest binary this is unlikely to occur. I think this is why we did not see this on mainnet and we are only seeing it on testnet.

[DavidBurkett]

Given 4.1.0 is the latest binary this is unlikely to occur.

It will occur for new Grin++ and Niffler nodes though, because Niffler is still 4.0.0 IIRC, and Grin++ won't be v3 for a few more months. So it would be nice to include this if we have a patch release going out soon.

[quentinlesceller]

Wow. Good catch 👍

[antiochp]

Given 4.1.0 is the latest binary this is unlikely to occur.

It will occur for new Grin++ and Niffler nodes though, because Niffler is still 4.0.0 IIRC, and Grin++ won't be v3 for a few more months. So it would be nice to include this if we have a patch release going out soon.

Yes. Planning to get a patch release out today to include this.